1. Field of the Invention
The present invention relates to a circuit breaker of a structure having the operating handle prevented from moving to the OFF position when the switching contacts are welded and facilitating the reset operation.
2. Description of the Background Art
The basic structure of a circuit breaker that will be described in detail afterwards with reference to the embodiment of the present invention is mainly constituted by switching contacts, a movable contact device with a movable contact of the switching contacts, a handle lever and a trip lever attached pivotally to a secured frame, a toggle link mechanism coupled between the trip lever and the movable contact device, an operating spring provided between the connecting pin of the toggle link and the handle lever, a latch device to latch the rotation of the trip lever by the operating spring, an overcurrent tripping device releasing the latch of the latch device to open the switching contacts when overcurrent flows, a reset means to reset the latch device released in its latch, a casing of molded insulator to enclose the above members, and an operating handle protruding from the casing.
The ON operation of this circuit breaker is performed by rotating the operating handle attached to the handle lever in the ON direction. This rotation causes the operating spring to extend. When the acting line of force of the operating spring crosses the connecting point of the trip lever and the toggle link mechanism, the bending toggle link mechanism is straightened, whereby the movable contact device operates. As a result, the switching contacts form contact. The OFF operation is performed by rotating the operating handle in the OFF direction. This rotation causes the operating spring to extend. When the acting line of force of the operating spring crosses the connecting point between the trip lever and the toggle link mechanism, the toggle link mechanism taking a straightened posture is bent, whereby the movable contact device operates to open the switching contacts.
In a trip operation when the overcurrent tripping device operates in an ON state, the latch of the latch device is released. The trip lever rotates, whereby the connecting point between the trip lever and the toggle link mechanism moves. When the acting line of force of the operating spring relatively crosses this connecting point, the toggle link mechanism taking a straightened posture is bent, whereby the switching contacts open. Here, the handle lever is rotated to a position intermediate the ON position and the OFF position. In order to close the switching contacts of the circuit breaker subjected to a trip operation again, the handle lever is moved towards the OFF position to perform a reset operation of turning the trip lever that co-acts with the handle lever to the direction where the latch means attains an engaging state again. By this operation, the operating handle passes the reset position to return to the OFF position. Subsequently, the switching contacts can be brought into contact by effecting an ON operation as described above.
Since the circuit breaker can have the operating handle move to the ON position, the OFF position, and a trip position intermediate therebetween, discrimination can be made whether the switching contacts are in contact or not by the position of the handle.
However, once the switching contacts are welded, the switching contacts will not open even if the operating handle is moved to the OFF position, resulting in a charging state of the load side of the electric circuit. This means that the electric circuit of the load side is in a charging state even when confirmation is made that the handle is located at the OFF position. There is a danger that the service and maintenance task may be being carried out in a charging state.
In view of the above problem, several circuit breakers have been disclosed (Japanese Patent Laying-Open Nos. 58-201221, 58-201222, and 58-201223). In brief, this conventional art is directed to a circuit breaker that, when an attempt is made to move the operating handle towards the OFF position in the event of the switching contacts being welded, the handle lever engages directly with the movable contact device at an intermediate position during its shift to the OFF position to prevent any further movement.
The problem related to the aforementioned danger is solved in these conventional circuit breakers. However, it is to be noted that in the reset operation of rendering the latch device released in its latch by a trip operation to an engaging state again in the conventional circuit breaker, the trip lever is rotated in the reset direction while the reset member fixed at the handle lever slides along the engaging end of the trip lever. Consequently, a bigger operating force is required in the reset operation due to the friction generated by the slide